Zero-phonon lines in the photoluminescence spectra of MgO:Mn²⁺ nanocrystals

We report the observation of a pair of sharp zero-phonon lines in MgO:Mn²⁺ nanocrystals, which appear simultaneously in photoluminescence. We suggest a reason why these lines have not yet been observed in the system in question even in the bulk material, but appear in nanocrystals synthesized by combustion. The easiness of the excitation of extremely sharp zero-phonon lines makes our finding attractive for optical nanodevice applications.